During the past year the following areas were investigated: 1. Dopamine Agonist Potencies of Ergolines: The dopamine agonist potencies of several ergoline derivatives belonging to a homologous series were tested. The ergolines are potent displacers of H3 -dopamine and H3 -spiroperidol binding from striatal membrane sites, cause rotational behavior in rats with lesions of the nigro-striatal dopamine pathway, and relieve tremor in monkeys with ventromedial tegmental lesions. The potencies of ergolines for displacing H3 -DA binding from striatal membrane sites and for their effectiveness in two different behavioral tests for DA agonists can be ranked in the following order: N-propyl greater than N-ethyl greater than N-methyl. The repeated administration of the long acting ergoline derivative, pergolide, causes a decrease in the total number of striatal binding sites for H3 -spiroperidol. 2. Distribution of Substance P-Like Immunoreactivity in the Central Nervous System: A comparison of the distribution of material reacting with antisera to substance P and tyrosine hydroxylase, respectively, was made on adjacent sections of the central nervous system of untreated rats using Co n's indirect immunofluorescence technique. All catecholamine-containing cell groups (A-A15) were surrounded by substance P-positive nerve terminals. A very high or high density of substance P-containing fibers was observed around the A9 dopaminergic cells and their dendrites in the substantia nigra and around the A2 catecholamine-containing cells in the nucleus commissuralis. There are certain areas where both substance P and tyrosine hydroxylase immunoreactive terminal networks were seen including the medial frontal cortex, caudate nucleus and the nucleus accumbens. The results suggest that substance P-containing nerve terminals may innervate catecholamine-containing cells and substance P-containing and catecholamine-containing nerve terminals may together influence neuronal activity in certain brain regions.